Justin Bieber has given director Lee Hirsch's controversial new movie Bully a big box office boost by donating a new song for the film's trailer.

The singer was among the celebrities petitioning for officials at the Motion Picture Association of America to drop Bully's R rating so more teenagers could see the hard-hitting film.

The movie has now been re-edited to secure a PG-13 rating and Bieber is helping to spread the word about the project, which chronicles the bullying epidemic in America's schools, by allowing Hirsch to use his new Diane Warren-penned tune, Born to be Somebody, in advertisements.

The teenage pop sensation says, "My fans are always for supporting a great cause. It's one of the things I'm most proud of as an entertainer. I hope they see Bully with their friends and help start the conversation so we can end bullying."

The TV ad featuring Bieber's song premiered on Fandango.com on Monday.

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